Field Methods for Navigation and Mapping in Challenging Terrain

1. Field Methods 2 • When a GPS only won’t do: • Forestry canopies • Canyons (no reception or can’t reach) • Underwater • Small areas when you don’t have a sub-meter GPS • You can see but can’t get to the features • Bottom of a canyon • Across a stream • Part way up a clif

2. Definitions • Bearing – direction to target (a.k.a. azimuth) • Typically measured with a compass • Heading – direction of travel • Note: A GPS provides a heading while you’re moving by finding the angle between your current location and a previous one. Because of this, it’s accuracy is poor and unreliable.

3. Basic Idea • Establish a “station” (a.k.a. benchmark) with more than adequate certainty • “Shoot” “meets and bounds” to points • Measure direction and distance • Convert to coordinates • Must use a projected system! • E.g. UTM, State Plane • Accuracy decreases as you move from point to point.

4. A little trig… New Coordinate (x2,y2) dx North dy D Given: - (x1,y1) and Compute: - (x2,y2) Existing Coordinate (x1,y1) Note: This only works in projected systems and there will always be error

5. Compasses • The earth has a magnetic field that has a “north pole” and a “south pole” just like typical magnets • We can use this field and something that is magnetized to orient ourselves just about anywhere on the earth.

6. Field Compass How to use a compass

7. Finding Direction • Point the “Direction of Travel-Arrow” in the direction you want to go • Turn the compass housing to make the north arrow (red part of the compass needle) line up with the orienting needle. • Check the direction of travel arrow again • Record the angle that is next to the direction of travel arrow • Add the appropriate amount of declination

8. Mirror-sighting Compass Wilderness Learning Center

9. Declination • “North” is not magnetic north • Compasses measure magnetic north (approximately) • See: Wiki page at: • https://en.wikipedia.org/wiki/Magnetic_declination • Check out the cool animation on how declination has changed • Find out declination at: • http://www.ngdc.noaa.gov/geomag-web/

10. Declination • If we measure 0 degrees on a compass, the actually point is off by the “declination”. • We must add the declination to all our angles • Try it and check on a map

11. Measuring Distance • Best: • Laser distance measuring tool • Next best: • A lightweight measuring tape • Worst: • Pacing

12. Distance with a Range Finder The range finder will calculate the horizontal and vertical distance for you.

13. Leveling Rod • Without a leveling rod, inclinations and horizontal distances will be incorrect • Can also adjust later

14. Laser Range Finder From Laser Tech’s user’s manual

15. Taking a Horizontal Distance • Press the “Fire” button to turn on the range finder • The display panel should show “HD” for “Horizontal Distance”. • If not, press “Forward” until you see “HD”. Laser Tech Inc.

16. Taking a Horizontal Distance • Point the range finder at a target. • Press “Fire” to turn on the laser pointer. • Press and hold “Fire” until you hear a beep • Release “Fire” you should see a distance. • Record the distance including the units “F” for feet, “M” for meters • Take another measurement by pressing “Fire”. • When done, press “Forward” and “Back” at the same time to turn off the range finder.

17. Taking a Horizontal Distance • If the display shows “EO 1”, you did not get a good signal back from the target. • Try again or use the reflector on a pole. • See the user’s manual for more information.

18. Taking other Measurements • Turn on the range finder. • Use forward until “INC” is displayed • Press “Fire” and record the inclination value • Use forward until “HT” is displayed • Press “Fire and record the height value

19. Additional Resources • 1-page guide from SFSU

20. Additional Slides

21. Note: the range finder appears to only take measurements if the target is very white or you used the included target.